For over 30 years the Seychelles Child Development Study (SCDS) has focused on examining the potential developmental risks associated with low-level methylmercury (MeHg) exposure stemming from daily ocean fish consumption during pregnancy, an issue of high public health significance. Our studies of over 3,000 participants have shown that nutrients, genetics, and maternal immune function play an important role. These findings provide important clues towards better understanding mechanisms of low-level MeHg toxicity and factors that may influence susceptibility. Our international research consortium includes four key partners with expertise in toxicology, epidemiology, biostatistics, nutritional biochemistry, and human genetics. The SCDS is a unique source of longitudinal data with extensive information on biomarkers and population characteristics. It is imperative that this resource is preserved, thoroughly documented, and enriched to realize its long-term scientific potential. The proposed study will lay the foundation for continued, integrative and translational science examining MeHg toxicity mechanisms and the long-term dynamics of low-level MeHg exposure. The current proposal has three specific aims. First, we will enrich the biorepository and outcomes database of the NC2 cohort for future studies of underlying mechanisms of MeHg toxicity and clinically-relevant phenotypes. We will re-examine 1,457 Nutrition Cohort 2 (NC2) participants who were recruited in 2008-2011 and are currently undergoing a 7-year examination. We will obtain hair and blood samples for future studies focusing on mechanisms of MeHg metabolism and toxicity. We will also collect data on medical history, sociodemographic factors, anthropometrics measures, health behaviors, and fish consumption, and we will link our study records with school examination records. Second, we will enrich the biorepository and outcome database of Main cohort study participants and their mothers to establish baseline data for novel prospective studies of MeHg toxicity across the life course. We will re-enroll the Main cohort (n=615; recruited in 1989-1990 and followed for 24 years) and their mothers (n=622, recruited in 1989-1990 and re- enrolled in 2013) and update data on health behaviors, sociodemographic factors, medical history, anthropometric measures, and fish consumption. We will collect hair and blood samples, and measure hair MeHg levels to estimate exposure across 30 years of follow up. In the Main cohort we will examine markers of autoimmune responses and correlate them with life course MeHg exposure estimates. Mothers will complete a brief assessment of physical and cognitive functioning. Finally, we will facilitate data access and sharing through improved data harmonization and discovery. We will develop an online Data Access Request and Visualization Application that will consist of a standardized data dictionary across all SCDS cohorts. It will allow users to explore our data through the visualization of descriptive statistics, and to request data and samples.